Method of insulating electrical conductors



Aug.k4, 1942.. H. GQHALL Erm. 2,291,961

METHOD 0F' INSULATING ELECTRICAL' coNDUoToRs Filed March 18, 19:59 2 sheets-sheet 1 HARRY G. HALL LASZLO l. KOMIVES INVENTORS ATTORNEY Aug. 4, 1942.

METHOD 0F INSULATING ELECTRICAL CONDUCTORS H. G. HALLl ET AL Filed March 18, 1959 Fla-2 FlGfB Y 2 Sheets-Sheet 2 HARRY G. HALL LASZLO I. KOMIVES WMA Ahn Patented Aug.` 4, 1942 METHOD oF msULATlNG ELECTRICAL CONDUcroas Harry G. Hall and Laszlo I. Komives, Detroit,

` Mich., assignors, by mesne assignments,l to Hercules Powder Company, Wilmington, Del., a corporation of Delaware Application March 18, 1939, Serial N0. 262,614

- 3 Claims.1 (Gl. 174-19) This invention relatesto a method of insulating an electrical conductor and more particularly to a method of insulating high tension cable conductors at points where the conductors are joined or where they are terminated in order to attach them to switches and other apparatus.

The prior art has always experienced some dimcuity with migration ofthe oil, with which the paper insulation on the cables has been impregnated, in the early installations where low potentials were utilized. 'I'his proved to be troublesome but was considered to be more or less a nuisance and not worth spending money to eliminate. However, as the art has gone to higher and higher potentials and the viscosity of the impregnating compounds has been constantly decreased in order to obtain lower dielectric losses, the frequency of oilfmigration 1ncreased and within the past 10 years or so has become a critical factor in cable` installations. It has been especially true on high tension cable systems, where so-called hard lling compounds, have been used on cable accessories such as joints.

terminals, etc.

Prior art filling compounds when used 'in cable joints, for example, have all had a tendency to dissolve in the oils with which the paper insulation used on cables has been impregnated.

This oil solubility has resulted 4in innumerable failures on the high tension cable lines because of swollen, collapsed or burst joint sleeves. Solu- 4tion of the joint-filling compoundin the cable oil has materially increased the power factor and dielectric loss of the cable to a point where failures haveoccurred in the cable due to heating ofy insulation, because of migration of the dissolved fllling compound into the cable. Furthermore, once a compound is dissolved in the joint;A

a channel may exist thru the Joint which may allow oil todrain from the cable at higher points and thus cause cable failure because of imper-A fectly impregnated cable at such locations.

The trouble with oil migration from terminal boxes into the cables has also become critical duringthe last few years, especially'with high tension installations. High power factor and dlelectric loss may 'reslt when oils of different cable and thus displacing the heavier oils with which the paper insulation is impregnated to the detriment of both the cable and the terminal.

It is an object of this invention to provide a method whereby joint failures, due to the oil solubility aof the insulating compound used in making the joint, are substantially completely obviated. v

It is a further object of this invention to provide a means for preventing the migration of mineral oil from cable terminals into the paper `insulation of the cable.

Further objects of this invention will appear hereinafter.

These objects are accomplished by the following invention which consists broadly of providing a'method of insulating electrical conductors by surrounding said electrical conductors with a hollow body and substantially filling the space intervening between the conductors and Walls of said ho'llow .body for at least a portion of the total length of said hollow body, with an insulating composition comprising a mixture of a natural glyceride and v petroleum hydrocarbon-insoluble resin derived from pine wood.

Having now indicated in a general way the nature and purpose of this invention, there follows a more detailed description of the preferred embodiments thereof with reference to the accompanying drawings in which:

lFigure 1 represents a view of a cable joint, partly in cross section.

Figures 2 and 3 show themethod of using the insulating compound in accordance with this invention for insulating electrical a cable terminal box.

Figure 4 represents an alternative method which may be used for insulated electrical conductors in a cable terminal box. The method here shown, however, is limited to insulations in a cable terminal which is in a vertical position.

Referring now particularly to Figure y1 the from for a distance back to the end of each to allow suitable manipulation. Various layers of oil-impregnated paper insulation 2 are removed from the conductors, laying bare the cable conductors 3.- The cable conductors are so arranged that the ends of the bare copper are held squarely together by a soft copper sleeve 4 of a diameter soinrt'vhat more than the conductor 3 and of sufficient length to extend far enough over the joint to make substantial mechanical and terminal'from'soakinglnto the insulation of the 55 electrical contact. The ends of sleeve 4 are filed conductors in so as not to leave any sharp edges, then carefully hammered down 'in order to nt snugly, filed smooth and then sleeve 4 is soldered to conductors l. ,l

After the conductora have been Joined. a lead sleevelofalargesectionwithrespeettothe lead sheathed rcable and of sullioient length so that the ends thereof extend appreciably beyond the point where the cables have been opened, is then placed over the joint. Lead sleeve l is fastened to the lead sheathed cable I by applying a wiped solder Joint U to each end of sleeve I. Leadsleevelisthennlledwithahotcomposition 1 at a temperature sumciently hlsh to have the resin present in a molten state, comprising a natural glyceride and. petroleum hydrocarboninsoluble resin derived from pine wood, and after cooling of this insulating composition, sleeve l is sealed, by soldering, or in any other manner well knowny to the art.

This invention relates particularly to a method of insulating conductors in a cable terminal box'. TheembodimentshowninFigures2and3is especially adapd for use where the end of the cable enters the cable terminal box horisontally. Referring particularly to Figure 2, lead sheathed, paper insulated. multi-conductor cable i is inserted horizontally thru one side of cable terminalbox i2,onlyaportionthereofbeingshown. said cable il being fastened to cable terminal box ilinthemannershownorinanyother mannerwell knowntothe art. Ileadsheathing is then removed from a portion of cable Il which projects into cable terminal box Il, exposing the paper insulated conductors il, for a distance depending on the voltage at which cable Il is' to 0perate. The paper insulated conductors i8 are then wrapped with an insulating ttl Il which is coated or impregnated with an insulating composition comprising a natural glyceride and petroleum hydrocarbon-insoluble resin derived from pine wood-taking particular care to cover allof the exposed paper insulation on the conductors. In most cases, it will be desirable to have a multiplicity of layers of tape.` A iiexible glove il made of rubber or of similar material capable ofbeingreadily shapedtoconi'ormtothe spaced arrangement of the conductors is then placed over conductors I8 leaving a thumb i. of glove il free. 'lhe fingers of glove Il are open attheendandtheendsofthetlngersengaging the insulated conductors il are then wrapped with cord -to form al tight Joint with the insulation. 'Ihe wrist of glove il is similarly wound to the lead sheath of cable Il.

A hot composition, |71 ata temperature suiilciently high to have the resin present in a molten state, comprising a namral glyceride and petroleum hydrocarbon-insoluble resin derived frompinewoodisthenpouredinthroughthumb v It nllingthe glove withsaidcomposition. After the composition I'I has cooled, thumb i0 os glove ilisfoldeddownandtiedasshowniniguxes and then several layers of tape coated or impregnated with insulating composition l'l applied `about the glows il. Cable terminal box il is then filled with an insulating oil, for example. a suitable mineral oil. Because of the insolubility of our insulating composition in mineral oil. a

complete stop is provided which prevents the mineral oil from entering the paper insulation ofcable il.

Although, as stated before the method above described is particularly applicable for usewhexe the cable enters the box horizontally. it is also 75 nl `aneifectivesill'lpisprcvvidfedtothemigration xnalinel'allnilartothaiiili'liiitliltislli'mightiril thesideoftheboxasshowninFiguresZandS. Thelead sheathingoncable llisthen removed, exposing the paper insulated conductors for a distance depending on the voltage at which thev cable is to operate. These paper insulated connlled with a suitable insulatingcompositimas, for example, a suitable mineral oil. our insulating composition, which is at the tom of cable terminal box, is insoluble in castor oil, either raw, blown or polymerized is preferred, as this compound is most resistant for long periods to the action of petroleum hydrocarbons such as will be present in mineral oils and in impregnated paper insulated cables.

Although any procedure maybe used to combine the resin and oil, we prefer to combine and vblend the oil and the petroleum hydrocarbon-insoluble resin derived from pine wood by fusing this resin at fa temperature slightly above its melting point and then adding and thoroughly admixing with this fused resin the desired amount of the oil. After mixing, the mixture may be allowed to cool and may be used from time to time merely by reheating to the point where the combination is fluid. For the purposes of the present invention, we prefer to have the compound at a temperature of approximately 250 F. when pouring the composition into theexible glove or into the lead sleeve.

Inorder to show the particular effectiveness of the insulating compositiohs made in accordance with the present invention, the following data are shown. Four compounds were made, varying the amount of petroleum hydrocarbon-insoL uble pin wood resin in each case. The oil-resin mixturesvwere prepared by adding the resin to the oi1 gradually. During the mixing, which required from 2 to 4 hours, the mixtures were kept nat-a temperature of100" C. to 130 C. and were mechanically stirred. These mixtures, to which we shall hereinafter refer as A, B, C, and D had the following composition in per cent by weight.

Per cent hpedtrwleut Pez cenitl I y 0cm' nmoro Mixture insoluble (cold pine wood Dressed) .3 resin A small weighed crucible filled with each of these compounds was then immersed in individual asks containing 150 rnl. of unused insu-lating oil. 'Thse flasks together with the crucibles were kept in an oven at 65 C. for one wek after which the cruc'ibles were removed, wiped free from oil with a dry' cloth, and reweighed, the loss in weight measuring the solubility of the compounds in the oil. A power factor test was then made on the oil to determine the extent of dam- The um obtained are shown in the renewing table:

Tam.: I

Compound A B C D .5

Btittleness point ..F. lli-m Below 0 Below 0 Below 0 Solubility in oil at 65 C.

Lossin wt. of cpd per cent-. 0.06 0. 31 0. 0l Power factor of oil ai immersion of cpd.n 0.0030 0.(1118 0.0013 04113) Power factor of oil before immersion 0. 0014 Not determined-too fluid. "Power factor measured at .l C. ata voltage stress of 50 volts per mi The above table clearly shows the insoiubiiity v can be considered to be so small as to be negligible 4for all practical purposes. Solubility of prior art joint filling compositions in the insulating oil caused the power factor of the oil to increase enormously and this hasL been one of the maost serious disadvantages of prior art compounds. This disadvantage is. however, completely overcome by the present joint filling compounds.

In the following table, the eect on the power factor of an insulating oil is shown, by the addition thereto of minor amounts of a joint filling compound. The power factor measurements, as in the previous table, were made at a voltage stress of 50 volts per mil.

TABLE II v Power factor Percent compouiilidiin insulating 20 C. 40 C. 60 C. 80 C.

Insulating oil alone. 0.0002 0.0004 0.0012 0.0024 0.5 mixture 0.04 0.(I)11 0.0051 0.0098 0.5 as haltlc cdi* 0.1 214 0.2790, 0. 5012 0.7217 1. o o 1:1 cabe impregnating cpd. and mixtureB 0.0001 .0.0002 0.0007V l 0.0021

Compound completely solubleinthe oil. l

The remarkable superiority of the Joint illing compounds used in the present invention over prior art compounds is clearly indicated by the above table. The petroleum hydrocarbon-insol uble pine wood resin-glyceride-oil compositions of the present invention are so insoluble in the electrical insulating oil that their presencea has no deleterious effects on the electrical characteristics of these oils.

In the following Tables IH and IV'. various electrical characteristics are given of the compositions formulated as before shown.

' TABLE III Dielectric strength of mixtures A, B, C, aigd D (A. S. T.`M.,D17636T) v I lreakdown volti Dielectric strength age kilovolts 1h05 volts per mil Mixture "mh gap s eoo.eoo.ooo.eo.eoo.wo.

A 65.2 42.8 26.6 1,304 856 530 B 41. 5 29. 3 22. 2 830 586 444 C 28. 5 22. 3 18. 5 570 448 370 D 22.8 21.2 12.5 466 424 250 .l Tasas IV Power factor o; umm .4. s. c. and n (measand at 60 cycles and voltage stress of 2.82 volts per mil) Poweria'cior Mixture application of insulating tape over the conductors at the joint. which has been essential 'in all of the prior art cable Joints.

Furthermore, as the data before show, the petroleum hydrocarbon-insoluble pine wood resin-glyceride oil combinations, because of their insolubility in the oils commonly used in electrical work, make possible a joint which has for all practicalpurposes an indefinite life. On the other hand, prior art Joint illling compounds were all more or less miscible with the cable oils. As these materials mixed, the power factor increased with a consequent rise in temperature producing ultimately a cable failure. By preparing Joints in accordance with the present invention the possibility of Joint failure is practically ellminlted.

While it is possible by prior art methods to prevent oil from entering the conductor insulation on a three conductor cable. for example. in acableterminalinstallatiomtoraperiodof time, there is no assurance that the installation will remain tight during the lite of the equipment. This, as ,the data before clearly show, has been accomplished by utilising methods in accordance with this invention.

In connection with cable terminal installations. the oil idghtness of the open cable crosssection other-than the conductor insulation itseltisanevenmorediiiicultundertakingbecause of the uneven configurations which have to be taken into account. Due to repeated coolingandheating of theline.therelativevlition of the three conductors at the end o! the cable changed quite considerably and caused holes to be formed in prior art tapints which to outside appearances and even'under tests, appeared to be oil tight. To compensate for this movement. itisnecessarytohavethesleeveortaping around the conductors surrounded by a plastic compound held in position with an elastic material. Thisismccessfullyaceomplishedbythe method inaccordance withourinventionbecause ourl insulating compositionremains plastic atailoperatingtemperatiuessnditissurroundedbyacxibleglovewhichiselasdcandinitselfoiiresistant.

Itwillbeunderstcod thatwherewerefer toaneiectricalconductonwemeaneitberasingie conductor or multiple conductors.

Itwillbenn'therunderstoodthatihedetaill lgiven hereinbefore are illustrative only and in no way limiting on our invention as broadly describedhereinbeforeandintheappendedciaims.

What we claim anddesiretoprotectbyliettsrs Patent is:

1. a method of terminating an electrical cable inacsbleterminalboasaidcablecomprisinga plurality of conductors each of which is insulated with an oil-permeable insulation. which comprises fitting the cablereceivingportionofa de xible casing around said cabh and tting the conductor receiving portions of said casing around said insulated conductors. filling said oasing with a fluid oil-resistant insulating composition comprising amixtureofa natural glyoerida and a petroleum hydrocarbon insoluble resin derived from pine wood, wrapping said casing with servings impregnated with said insulated composition, andfillingthe cable terminalbox withan insulating oil.

2. In a cable terminal structure. the combination o! a cable comprising a plurality of conduce tors each of which is insulated with an oil-per meable insulation, a iiexible'casing including a pour opening and a plurality of tubular conductor receiving portions and a tubular cable recdving portion receiving said cable and conductors in such manner that the cable receiving portion ofsaidcasingreceivesaportionofsaidcabb and the conductor receiving portions receive a portion of the conductors, an oil-resistant insulating composition comprising a mixture of a natural glyceride and a petroleum hydrocarbon insoluble resin derived from pine wood nlling the space between said casing and said cable and conductors. s terminal box enclosing said casing. andaninsulatingoiinllingthespacebetween said casing and said terminal box.

3. Amethodoi'sealingtheinsulatingmaterial oi an electrical cable against migration loss. said cable comprising a plurality of conductora spreading from one end of said cable and being including a pour opening, a cable receiving portion and a plurality of conductor receiving porconduetors. securing the terporons in close fitting relalowing said mixture to solidify, whereby the oil of saidmaterial issealedandheldininsulatinl position.

l HARRY G. HALL.

LABZDO I. KOMIVIB. 

